I recently acquired a Japanese R8 shank face mill, and went to use it on the Novakon. However, the drawbar would not hook up. In investigation showed that the R8 shank was about .25' shorter than my collets, and as well the internal threads are deeper than normal. When I got the mill I had a similar problem with collets, and solved it by reducing the length of the spacer that screws into the top of the spindle.

Not wanting to do so this time, my idea was to remove the spacer, and then slide a 1/2-20 nut over the drawbar. This let the drawbar screw into the face mill shank. When done with that op I just replaced the spacer.